Hint: Use the database definitions inside of DBeaver/DataGrip/AnythingElse to see what can or cannot be NULL

AC:

• Update BackgroundTask.java to use Optional<?> for any fields that may be NULL
• Update BackgroundTaskRepository to use Optional<?> for any methods that may or may not return something back
• Update call-sites everywhere
• Ensure that there are no bugs and that all situations are correctly covered